In one conventional approach to pipe ramming, a percussive pneumatic hammer is used to drive the pipe horizontally or at an angle into the ground. The hammer housing is attached to the end of the pipe by means of a suitable fitting and is sometimes further secured by cables. A piston-actuated ram strikes a plate inside the housing and the percussive force is transmitted to the end of the pipe through the housing, thereby causing the pipe to advance into the ground. Friction between the soil and the pipe prevents backward displacement of the pipe while the piston retracts for the next strike. A typical small pneumatic hammer offers 0.17 kJ of energy and delivers 580 blows per minute, weighing less than 10 kg. A typical large hammer has 40 kJ of energy, weighs 12 metric tons and delivers 180 blows per minute.
Hydraulic (rather than pneumatic) hammers are often used in vertical drilling. Hydraulic hammers generally operate at fewer strokes per minute but delivering much more per blow. One hydraulic hammer weighs 4 metric tons, delivers 65 blows per minute at 30 kJ, while a 242 metric ton hammer delivers 2300 kJ at 30 blows per minute. In many hydraulic hammers, the energy per stroke and the strike rate are adjustable. The strike piston extends outside the hammer housing to strike the casing. In vertical drilling, the hammer housing is maintained in contact against the casing principally by means of gravity, though a winch crowd system may also be used for enhanced crowd.
It is also known to use hydraulic percussive hammers disposed horizontally for pipe ramming. Hydraulic hammers provide greater force and the ability to adjust the impact force of a hydraulic hammer allows for tailoring of the system to the soil conditions. However because the ram extends outside the hammer housing, it is not practical to secure the housing to the pipe. It therefore becomes essential to provide crowd of the hammer against the pipe. One approach to doing so is disclosed by Verkyk, U.S. Pat. No. 6,652,190, who relies on a cable winch crowd system (illustrated in FIG. 1A of Verkyk and reproduced as FIG. 1 herein). While the system is reasonably effective in operation, it is unwieldy to set up, taking about a week to do so. The highly tensioned cables also present a significant danger to personnel.
It is an object of the present invention to provide a horizontal pipe ramming system with hydraulic crowd.
It is a further object of the invention to provide a horizontal pipe ramming system that uses a hydraulic hammer and that has an improved crowd system.
These and other objects of the invention will be better understood by reference to the detailed description of the preferred embodiment which follows. Note that the objects referred to above are statements of what motivated the invention rather than promises. Not all of the objects are necessarily met by all embodiments of the invention described below or by the invention defined by each of the claims.